Abrasive sheet material



Reissued Feb. 4, 1930 Rel 17,580-

UNITED' STATES PATENT OFFICE GUSTAVE E. BEER, JR., OF BROOKLYN, NEW YORK, ASSIGNOR, BY MESNE ASSIGN- MEN'IS, TO MINNESOTA MINING & MANUFACTURING COMPANY, OF ST. PAUL, m- I N'ESO'I.A,':A- CORPORATION OF MINNESOTA.

I snimsrvn snnn'r MATERIAL No Drawing. Original No. 1,645,087,. dated October 1 1, 1927, Serial No. 581,275, filed August 11, 1922.

' Application for reissue filed October 10, 1929. Serial No. 398,806..

I the like, according to the kind of coating and the sheet material which carries it. The object is the improvement of goods of this class and of their method of manufacture, and especially the production of a superior and sat- IQ isfactory quality of waterproof sandpaper by which is meant sandpaper or abrasive sheet material which is not only superior in cutting quality and durability to the common -or non-waterproof variety but which can be used Wet with water, with still greater efficiency and without impairing or loosening the adhesive which holds the grit or unduly softening or affecting the paper base, and which is tough and pliant and does not become "brittle with age and which can also be made to sell within the established price range of goods of this class.

In the preferred form ofemy invention, as applied for making sandpaper, I proceed as follows: The plain paper stock or cloth, as the case may be, is first immersed in a bath of cotton-seed oil, thinned when necessary by the addition of benzine. The benzine or other thinner hastens impregnation of the oil intothe paper fibres, and is later allowed to volatilize. The paper is preferably fed in a continuous strip or ribbon through the oil bath and thence passes through a pair of squeegee rollers to remove any surplus. This operation may be done at ordinary room temperature and its purpose is to make the paper water repellent as later explained. The paper I thus treated and waterproofed is then, and if need be immediately, passed over a gluing roller, or through any other suitable means for applyin a coating of adhesive to one of its sides. The adhesive thus applied is a varnish of approximately the following compos'ition:

- Per cent Tung oil Linseed oil 8 Rosin -l 9 Mineral spirits and dryer 48 but the amountof spirits or other thinner is subject to variation according to the thickness of the coating, and that is determined to some extent by the size or grade of the grit to be applied, aswill be understood. The above roportions are by weight, as customary.

he paperis then doused or covered with the grit or abrasive material on the side carryin the fresh adhesive and then receives a secon or sizing coat of adhesive over the grit, as

customary. This sizing agent may be the same varnish as used for the main adhesive but is made somewhat thinner by the addition of benzine or other volatile-thinner, and more or less, according to the grade of grit as will also be understood'by those versed in this art.

The oiled paper now carrying the gritholding coating of adhesiveis next baked in an oven for a period of about sixteen hours at a temperature of about 200 F., or for a shorter t1me at a higher temperature but in any event, within the range of temperature commonl employed for setting baking varnishes. ometimes a preliminary baking for twohours or so is given after the sanding and before the sizing, which is preferable in the case of coarser grit. On removal from the oven the paper may be cut into sheets and is ready for sale. a

The baking drives off any volatile constituent left in the paper from the waterproofing bath and thickens but of course does not actually dry the'cotton-seed oil, and it also drives off the volatile thinner of the adhesive but more e'speciallyits effect and primary purpose isto indurate the solid body of the varnish and convert it into a permanently elastic, water-proof layer which isknown as non-drying or semi-dryin and if they are not naturally thin enough or quickly and thoroughly penetrating the paper base, they can be made so either by the addition of a-..volatile thinner as above explained or by heat. I prefer cotton-seed oil because while it is an excellent waterproofing agent, it does not in fact render the paper absolutely immune from the effect of moisture, as manifested by the fact that immersion for a few minutes in water gives the paper base a tougher and more leathery feel than when dry, although a many day immersion in hot water does it no damage whatever. Cottonseed oil is also preferred because it acquires from the baking, a permanently sticky or jelly-like consistency. This, however is not objectionable 'or noticeable in the product because the amount present is small and well distributed among the cellulose fibres, but its effect is to tie the fibres together with some freedom for relative slip ing of' one on" the other and without brea in as they would do if positively bonded, t us giving the paper base greater toughness and a permanent suppleness, or pliability. Other non-drying or seml-dryin oils possessing-these properties,

though per aps in a less degree are soya bean oil, lard oil and corn oil. ineral oils and greases are non-drying and therefore available, but are not so effective as waterproofing agents, but the selection of the agent. is naturally determined by the character of the baseand also and particularly by the character of the adhesive as presently explained and of course also .by the cost, be-

cause the cost afl'ects the-usefulness of the product. V

One of the re uirements of the varnish adhesive above re erred to is that its oily base shall be-a drying oil, that is to say, an oil that is naturally a dryin oil, or that is made so by the addition of ryer. Such an oil, especially when bodied with rosin or gum, is convertible by proper baking into a tough elastic solid practically waterproof. 'In general, any of the baking varnishes, of which there are many on the market, will be found to have its base composed rincipally of such oil and is .therefore suita le for use. A further re uirement is that such oil or the adhesive s all be miscible with the agent used for water-proofing, the fact being that an actual mixture or local solution occurs between'the adhesive and the water-proofing agent on, orunder the surface of the paper .or base. By reason of such solution or partial solution, the adhesive comes in direct contact with the cellulose fibres of the paper surface, thus gaini an opportunity to unite firmly thereto, whic cannot occur when the 'two agents are non-miscible, as for example,

in the case where it is attempted to secure animal lue which is not soluble in oil, to paper w ich has been soaked in oil. A tung oil varnish, of proportions about as above described, constitutes the preferred adhesive under the principle of this invention because,

1ylarge percentages of oils which are naturally drying like. linseed oil, or oils which are made so by the addition of dryers, and consequently all such materials are properly equivalents in principle to the functions of tung oil. The gum or rosin when used in the varnish gives it body and a desirable viscosity before baking, and tends to lessen the extent of baking necessary to. produce a given hardness of the adhesive. Smallv amounts between 5% and 15% by weight are generally sufficient for this purpose in most cases, the adhesive effect ,being principall if not entirely derived from the effect of aking the drying oil. Without gum, the same class of oils is available but may require bodying to secure the desired consistency to constitute an adhesive.

The duration and temperature, of the baking operation are coordinated more or less to the kind of varnish or oil but with any given varnish or oil the baking may be varied to secure the desired degree of softness or pliability in the product as -may be consideredbest for thekind of abrasive or surface coating that is used. Thus a short or moderate baking is generally best for fine grain sandpaper and a harder baking is for paper intended for more severe use. Thus an absolute control of the softness of the vantage of this invention and uite new in this art. The exact baking speci cations cannot be given forall cases-without reference to the kind of varnish and grade of grit but this is amatter easily determined by a very little experience. It will not be necessary to point out .that the baking operation is no different from the ordinary practice in the use of baking varnishes which is very well known, and is to be distinguished from the long established practice in the sand-paper art, of air-drying the freshly glued paper by exposing it tothe air in warmly heated rooms. The baking of the paper according to the requirements of thisinvention, which is carried on-at a. temperature in any eventabout -glue sand-paper would permanently impair the glue. v

Inasmuch as the attainment of a secure bond between the oily or waterproof paper fibres and the adhesive is the principal object,

'product'is available, which is a further ad- 7 it will be clear that the adhesive -mi'ght be applied first and the waterproofing agent afterwards andlikewise that the peculiar properties and virtues of the adhesive and water roofing agents will be independently mani ested by each even in the absence of the other, and all within the spirit and scope of principle thereor which has been above explamed.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. The method of making flexible abrasive sheet material consisting in combining with a suitable base, a waterproofing agent comprising cotton-seed oil impregnated into the bros thereof, and a separately applied gritholding coating of adhesive miscible with the cotton-seed oil and firmly bonded with the impregnated fibres;

2. The method of making flexible abrasive sheet material consisting in combining with a sheet cellulose base, a cotton-seed oil waterproofing agent and a tung oil .varnish in the form of a coating holding the grit and baking ata temperature above 140 F., thus making the coating tough, elastic and relatively pl able. v

3. Flexible abrasive sheet material comrising a suitable base and a grit, said base ing waterproofed with cotton-seed oil and a coating of baked tung-oil Varnish co-operating with the cotton seed oil in attaching the grit to the base.

4. Waterproof sandpaper comprising a paper base and'a grit, said base being treated with cotton-seed oil and with seperately applied adhesive coating attaching the grit thereto.

- 5. Flexible abrasive sheet material comprising a backing and a grit or layer of abrasive material secured to said backing by an adhesive composition comprising tung oil, linseed oil, 'rosin, and mineral spirits and dryerFbaked to a temperature of about 200 spirits and about 200 (gyer, baked a temperature of In testimony whereof, I have hereunto signed my name.

GUS

6. Flexible abrasive sheet material including a flexible backing, said backing being immersed and saturated with cotton-seed oil thinned by the addition thereto of benzine,

a grit or layer of abrasive particles secured TAvE E. BEHR, JR. 

